Here is a simple, simple example so you can see it and believe it:
1 A
;; A ;; A ;; A
2 B
;; B ;; B ;; B
3 C
;; C_a ;; C_a ;; C_a <<a-block>> <<b-block>> ;; C_z ;; C_z ;; C_z
4 D
;; D_a ;; D_a ;; D_a <<c-block>> ;; D_z ;; D_z ;; D_z
5 Tangled result
;; D_a ;; D_a ;; D_a ;; C_a ;; C_a ;; C_a ;; A ;; A ;; A ;; B ;; B ;; B ;; C_z ;; C_z ;; C_z ;; D_z ;; D_z ;; D_z
The source is here.